TPS65146 Datasheet, PDF (14/30 Pages) Texas Instruments – Compact LCD Bias IC with LDO, VCOM Buffer and Reset Function

TPS65146
SLVS869 – NOVEMBER 2008 ........................................................................................................................................................................................... www.ti.com
Setting the Output Voltage
The output voltage is set by an external resistor divider. Typically, a minimum current of 50 µA flowing through
the feedback divider is enough to cover the noise fluctuation. The resistors are then calculated as
V_S
R2 = ^Vref » 18 kΩ
70 μA
æ
R1 = R2 ´ _ç
V_S
ö
-1_÷
è ^Vref ø
R1
V_FB
R2
(2)
with V_ref = 1.240 V
Compensation (COMP)
The regulator loop can be compensated by adjusting the external components connected to the COMP pin. The
COMP pin is the output of the internal transconductance error amplifier. The compensation capacitor will adjust
the low frequency gain and the resistor value will adjust the high frequency gain. Lower output voltages require a
higher gain and therefore a lower compensation capacitor value. A good start, that will work for the majority of
the applications is C_COMP = 3.3 nF and R_COMP = 18 kΩ for a 3.3 V input.
Input Capacitor Selection
For good input voltage filtering low ESR ceramic capacitors are recommended. TPS65146 has an analog input
VIN. A 1-µF bypass is required as close as possible from VIN to GND.
One 10-µF ceramic input capacitor is sufficient for most of the applications. For better input voltage filtering this
value can be increased. Refer to Table 3 and typical applications for input capacitor recommendations.
Output Capacitor Selection
For best output voltage filtering a low ESR output capacitor is recommended. Two 10-µF ceramic output
capacitors work for most of the applications. Higher capacitor values can be used to improve the load transient
response. Refer to Table 3 for the selection of the output capacitor.
Table 3. Rectifier Input and Output Capacitor Selection
CAPACITOR
10 µF/0805
1 µF/0603
10 µF/1206
VOLTAGE
RATING
10 V
10 V
25 V
COMPONENT SUPPLIER COMPONENT CODE
Taiyo Yuden
Taiyo Yuden
Taiyo Yuden
LMK212 BJ 106KD
EMK107 BJ 105KA
TMK316 BJ 106ML
COMMENTS
Cin
VIN bypass
Cout
To calculate the output voltage ripple that following equations can be used:
V_{RIPPLE_C}
=
V_S - V_{IN ´} I_OUT
V_S ´ f C
V_{RIPPLE_C_ESR} = DI_L ´ R_{C_ESR}
(3)
V_{RIPPLE_C_ESR} can be neglected in many cases since ceramic capacitors provides very low ESR.
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